AUTHENTICITY JUDGMENT METHOD AND AUTHENTICITY JUDGING APPARATUS FOR RECORDING MEDIUM COMPOSED OF DIFFRACTION GRATING PIXEL

摘要

PROBLEM TO BE SOLVED: To perform authenticity judgment not based on diffracted light resulting from a recorded pattern but based on diffracted light resulting from pixel two-dimensional arrangement structure peculiar to a recording medium composed of diffraction grating pixels.

SOLUTION: An authenticity judgment method for the recording medium M in which a pattern is expressed by two-dimensionally regularly arranging pixels composed of diffraction gratings, is provided in which the recording medium M is irradiated with laser beams 6 of a predetermined wavelength, diffracted light 7 near zero-order diffracted light diffracted at least by the recording medium M is made incident on a screen 4, a range of an image of the diffracted light reflected on the screen 4 except an image of the diffracted light from the diffraction grating constituting the pixel is imaged, a high pass filter is applied to the obtained image to remove a diffracted light image which is based on periodicity of the pattern of the zero-order diffracted light and near the zero-order diffracted light expressed in the recording medium. The obtained image is judged whether it coincides with a judgment criterion prepared in advance to judge whether the recording medium M is true or false.

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